Stand-by lighting units are used to light adjacent areas when a power line loses power. Such units conventionally have batteries which power the units' lamps when the connected power line is out. The units are exposed to elevated ambient temperatures and these often shorten the service lives of the batteries and thus cause considerable expense.
While an electrically operated compressor type vapor phase refrigerated enclosure could be used to accomplish the cooling of a battery to its optimum rated performance temperature, there are certain applications where such systems do not perform well or are not permitted. As temperatures rise above ambient, the performance of electric motors, compressors, and controls become increasingly inhibited, and less dependable in proportion to the temperature rise. Furthermore, the use of mechanical methods of any type for cooling emergency lighting system batteries in high temperature environments in nuclear power plants is hampered by mechanical unreliability and U.S. Nuclear Regulatory Commission regulations. The absolute necessity for dependable performance is so demanding under USNRC guidelines that there is serious concern about use of mechanical devices of any form, including cooling fans, to assist in improving battery life expectancy in certain areas of nuclear powered electrical generating plants. This also applies to non-mechanically driven vapor phase gas refrigeration systems such as that used in the old Kelvinator refrigerators.
There are problems related to electrical storage battery performance that users must consider. A battery's performance is rated at a specific temperature, in the case of a lead-acid type, the most broadly used rechargeable battery, its performance is based on 77.degree. F. and for every 15.degree. F. rise above that battery life expectancy is reduced by one half. So in an environment whose average temperature is 122.degree. F. (77.degree.+3.times.15.degree.) the useful life is reduced to 1/8 of the design, and at 137.degree. F. average temperature, life expectancy is 1/16 of the original. Consequently, a battery with a five year normal life expectancy will last only 4 to 8 months in an environment whose temperature varies from 122.degree. to 137.degree. F. U.S. Nuclear Regulatory Agency regulation #10CFR part 50 appendix R requires emergency lighting in many plant areas where temperatures routinely exceed 100.degree. F. In some areas temperatures even reach 132.degree. F.
In many locations in nuclear power plants the problem is solved by locating the battery remotely from the lamps they serve. However, because failure of the electrical power source that serves the battery recharge system causes the emergency lights to illuminate, its universal application is restricted. Consequently, many plant areas require "living with the problem" and replacing units every few months.